COMPARE_ENGINE is used to define the type of comparison processing used in a COMPARE statement.

Syntax

/*+ COMPARE_ENGINE({ 'SIMPLESORT' | 'ASYNCSORT' | 'SYMMETRICHASH' | 'OUTERJOIN' })

Arguments

  • SIMPLESORT - A Single-threaded sorted compare.

  • ASYNCSORT - An Asynchronous sorted compare, sorted with single-threaded read but asynchronous, multi-threaded difference handling.

  • SYMMETRICHASH - Symmetric hash is unsorted with asynchronous, multi-threaded read and difference handling.

  • OUTERJOIN - Outer join, unsorted compare with full read of source and asynchronous, multi-threaded lookup of target.

Additional Information

  • SIMPLE and ASYNC Compares utilize the underlying databases to perform sorts. The performance of these sorts will depend on the properties of the table and database: index on the sort key, database memory, etc.

  • SYMMERTICHASH and OUTERJOIN compares do not ask the databases to sort, i.e. the source and target queries have no ORDER-BY clause. However, the symmetric hash can consume significant memory in the Cirro RDBMS agent, so this must be sized accordingly. The outer-join engine does not have the memory constraint but does need good indexes for the lookups.

Examples

See Also

  • [COMPARE_QUEUESIZE hint]

  • COMPARE summary

  • [COMPARE statement]

  • [COMPARE with inline functions]